Radiographic imaging detectors comprising an array of small sensors to capture a radiation-generated image are well known in the art. A collimated radiation beam is intensity modulated as it passes through a radiation-absorbing object and the transmitted beam as detected thus represents an inverted image of the absorption by the object, which in turn is related to the elemental composition, density, and thickness of the object.
The contrast and spatial resolution in captured X-ray images are deteriorated by X-rays scattered from the object being imaged. Anti-scatter grids or so-called Bucky grids, which absorb the scattered X-rays, while passing through the transmitted X-rays which have not interacted with the object, have been used extensively during a long period of time, see e.g. U.S. Pat. No. 1,164,987 issued to Bucky 1915, U.S. Pat. No. 6,181,773 B1 issued to Lee et al. 2001, and references therein. Typically, however, the Bucky grids are only capable of reducing the scatter to 30% or 20% of its total intensity. At the same time a Bucky grid also attenuates the undeflected transmitted X-rays.
Recently, more sophisticated approaches for reducing the amount of scattered X-rays have been developed using dual-detector or dual-energy methods, see U.S. Pat. No. 6,134,297 issued to Chao, and references therein.
Further, to improve contrast the broadband radiation from an X-ray tube is heavily filtered before being used for radiographic purposes. It is well known that at X-ray photon energies typically used, the photoelectric absorption is decreased as a power law as the X-ray photon energy increases, while the scattering is increased.
For soft tissue the photoelectric absorption is decreasing rapidly at energies above about 20 keV and this higher energy X-ray radiation does not contribute to the image recorded, but reduces the contrast in the image. Thus, higher energies are filtered out from the radiation. Of course, the elemental composition, density and thickness of the object determine the optimal choice of the photon energy.
Still further, lower energy X-ray radiation is almost completely absorbed in the tissue and thus does not contribute to the image as detected, but just adds to the radiation dose, to which the object is exposed. Thus, lower energies are also filtered out from the radiation and a narrowband radiation centered around 18 keV is typically employed for soft tissue applications such as e.g. mammography.
Finally, in all present X-ray detectors the efficiency to detect X-rays decreases rapidly with increasing X-ray energy. Furthermore, the position resolution decreases with increasing X-ray energy.